Fuel for combustion



Patented Dec. 30, 1941 UNITED STATES PATENT OFFICE rum. roa comaosrronNo Drawing. Application October 1, 1938,

Serial No. 232,799

11 Claims.

This invention relates, in general, to improvement of hydrocarbon fuelsfor efficient combustion in combustion engines. More specifically, thisinvention relates to economical fuels with suitable ignition qualitiesfor efficient combustion in high speed compression-ignition engines andmethods for the preparation of these fuels by addition, in smallproportions, of inexpensive chemical substances, such as elementalsulfur, to hydrocarbon fuels.

Combustion engines, more particularly, high speed compression-ignitionengines, are generally referred to by the name of their prototype, theDiesel engine. Hydrocarbon fuels which have been found most suitable forthese engines are crude oil distillates which are highly paraffinic, butthese fuels are limited in supply and relatively expensive.

In consideration of increasing power and fuel economy with eliminationof vibration harmful to the mechanism in the operation ofcompression-ignition engines, principally when the hydrocarbon fuelcontains insuflicient amounts of hydrocarbon compounds recognized asserving 7 these ends by virtue of their suitable ignition qualities, theaddition of various chemical substances to the fuels has been proposed.

Hydrocarbon compounds characterized by aromatic, other cyclic, andhighly unsaturated hydrocarbons have poor ignition qualities as Dieselengine fuel ingredients, following from the fact that hydrocarbon fuelscontaining a large proportion of these compounds fail to undergo promptand smooth combustion in reprwentative types of engines in whichunsuitable combustion is manifested by engine vibrations and annoyingfknocking" sounds. A poor ignition quality in a compression-ignitionengine fuel is most frequently exhibited by an excessive ignition lag,in other words, anexcessive delay between the beginning of fuelinjection into the combustion chamber of the engine and the point atwhich ignition of the fuel sets in. In contrast, the normal paramnhydrocarbon cetane, whichserves as a standard of high ignition of the S.A. E. Volunteer Group for Compression- Ignition Fuel Research,'has adesirable minimum ignition lag. Since the ignition lag of a blendconsisting of normal cetane and the-aromatic compound alpha-methylnaphthalene more of cetane'by volume in a blend with alphamethylnaphthalene, such an addition asent is .45 quality in Diesel fuel ratingby recommendation considered to have commerciallysignificant'effectiveness, provided the addition agent used is not verycostly in comparison with the value of the fuel.

Various attempts have been made to find substances effective forreducing knocking properties of Diesel fuels, but substances which havebeen found effective for this purpose are not altogether satisfactoryfrom all points of view 10 for commercial use. For example, ethylnitrate is suitably effective for promoting the ignition qualities of aDiesel fuel, but it has to be used in relatively expensive quantities,it lowers the fiasn point of the fuel, and is not stable in an 15undiluted state.

An object of this invention is to improve Diesel fuels by the additionof an agent which is very inexpensive, is stable in an undiluted state,and which does not-lower the flash point of the fuel. A further objectis to provide for the addition of an agent which can be efficientlyincorporated into the fuel where the fuel is being used so that the fuelcan be improved for any particular engine; Another related object is toprovide for a method of adding and modifying the ignition improvingagents of the classherein described so that corrosive action of theagent is satisfactorily reduced.

The novel addition agents of this invention are characterized ascontaining sulfur principally in a free or elemental form and withmodifications for diminishing any undesired corrosive action which mightaccompany the use of sulfur. Although it might seem that the increasingof the sulfur content of a fuel is harmful, it has become more recentlyrecognized that no relation exists between the sulfur content of thefuel and the amount of cylinder wear which takes place in enginesoperating at high temperatures, .and that no harm would result inmanytypes of Diesel engines, ven if the sulfur content of the fuel usedin such engines were as high as about 2% by weight. The percentages ofadded agents hereinafter referred to are also on a weight basis.

In accordance with the present invention, it

is also proposed to make modifications in the use of elementary sulfuras an addition agent to eliminate corrosive action when required. Theordinary Diesel fuels obtained as crude distillates containsubstantially no free sulfur, and many of the fuels have been subjectedto a pretreatment, such as hydrogenaflon, which lowers their sulfurcontent to alnegligible amount. Hence, the addition of free sulfur invery minor amounts necessary for the improvement of the fuels does notnecessarily give the fuels excessive sulfur contents. Free sulfur needbe added in amounts varying only from .01 to about 1% to 60 make amarked improvement in the ignition 'ance as the fuel in the test qualityof the oil by reducing the ignition lag or increasing the cetane numberof the fuel.

Such a small amount of added sulfur will not or associating the sulfurwith another element, a such as phosphorus, or an inorganic radical,such ment and replaced by the more efl'ective'free sulfur, which is insome ways less corrosive. The treatment for removing the organic sulfurcompounds may even be such as to leave active sulfur in the oil. Thecrude oil distillate may be treated with sodium plumbite and a certainexcess of free sulfur, for example, to eliminate objectionable organicsulfur compounds and leave a certain amount of free sulfur dissolved inthe oil. Also, a crude oil fraction may be merely heated in the presenceof a certain amount of added free sulfur. Other known methods forreducing the original total sulfur content of a crude fraction may beemployed.

' The effectiveness of free sulfur in raising the cetane number of ahydrocarbon fuel is illustrated-by the following tabulated results inwhich a crude distillate fuel containing added amounts of free sulfur iscompared with the unmodified fuel which has a total sulfur content of0.44%:

Fuel tests Peliilfient 8:1 C t s ur in a e we Cetane cetane numbernumber Colombian number increase gas oil The method of testing isdescribed in the S. A. E. Journal of June, 1936, page 225, and consistsin matching the performance of a test sample with blends of cetane andalpha-methyl naphthalene. The per cent by volume of cetane in the blendwith the alpha methyl naphthalene giving the same ignition quality testperformsample is taken as the cetane number rating of that fuel.

The cetane number improvement made by adding free sulfur to ahydrogenated fuel'having no appreciable sulfur. content, 1. e., only0.17% total, is shown in the following table:

In instances when it is desired to maintain the sulfur content of thefuel oil low while adding active sulfur for ignition qualiiwimprovement, this may be obtained by partly combining as an amino group.In such combinations or associations, the effectiveness of the sulfurmay be increased and corrosiveness diminished. The

free sulfur may be used in these combinations by being added to the oilwith elementary phosphorus, either of the red or yellow form, or withammonia, or a suitable ammonium compound, such as ammonium sulfides.

Also, elemental sulfur may be reacted to some extent with a reagentwhich combines with the sulfur prior to additioplto the oil. It has beenfound that sulfur combines with a small proportion of amino groups asinhexasulfamide which is believed to have a composition represented bythe formula SeNH: or SIBN3HI, a: being undetermined, and in thiscomposition produces almost the same cetane number increase as does freesulfur when added to a Diesel fuel, while having a much lower copperstrip corrosion action and higher solubility. To obtain a combination ofsulfur with the amino group, ammonia may be reacted with a sulfurchloride or sulfur may be reacted with ammonia. A convenient method usedto prepare hexasulfamide in good yields is one in which ammonia ispassed through a solution of sulfur monochloride in chloroform, thereaction mixture being cooled by heat exchange with a freezing mixturein the early part of the reaction to prevent violent reaction, and afterdarkening of color, being permitted to have an increase in temperature.The admission of am-. monia was continued until the reaction mixturecolor became salmon red. From the resulting reaction products, ammoniumchloride was filtered off. Alternatively, the ammonium chloride may beremoved by extraction with water. Other low boiling alkyl halidediluents, such as ethylene dichloride, may be used in place ofchloroform. With increase of temperature toward the end of the reaction,the yield of hexasulfide, forming a larger part of the reactionproducts, is increased while the undesired byproduct, sulfur nitride,which is unstable and relatively unsoluble in hydrocarbon oils, isreduced to a negligible amount.

It is possible to separate the combined sulfur and amine compound fromthe other reaction products so that it may be added alone to the Dieselfuel, or the sulfur reaction products, in-- cluding free sulfur, may beadded together to the oil. Hexasulfamide crystals may be recovered fromthe chloroform solution in which it is prepared by fractionalcrystallization due to the relatively greater solubility of thehexasulfamide in organic solvents. For example, the chloroform solutionis first evaporated down to about a fourth of ,its original volume,then, upon addition of ethyl alcohol, in excess, a by-product comprisingsome free sulfur comes out of solution. After filtering off theby-product precipitate, re'concentrating the nitrate, and diluting theconcentrate with benzene, hexasulfamide is crystallized out from thebenzene by addition of aqueous alcohol. Purified hexasulfamide, obtainedby recrystallization, is insoluble in and stable towards water,odorless, non-explosive, and stable "to air. Cetane number tests on aDiesel ,oil composed of a Colombian gas oil and containing only 1.5% ofthe aminated sulfur show that this addition agent gives the fuel acetane number increase of +10 or +11.

A similar cetane number increase is obtained when phosphorized sulfur,which is believed to have preferably the composition of phosphorussesquisulfide, P4S3, is added in a concentration of less than 1% to a 40cetane number Colombian gas oil. The free sulfur undergoes reaction witheither yellow or red phosphorus when heated together to form variousphosphorus polysulfides. The phosphorus polysulfide is somewhatdifficult to dissolve in the oil except by heating the oil. Solubilizingmethods may be used, for example,- boiling of the phosphorus polysulfidein alcohols with which the phosphorus and sulfur are believed to undergoreaction to some extent, forming associations or complex compounds whichmight be identified as alkoxyphosphopolysulfides, and which dissolvemore readily in liquid hydrocarbon fuels at normal temperatures. Thephosphorus sesquisulfide, on being dissolved into a heated fuel oil isnoted to form an opalescent colloidal suspension which, however, isfairly stablein the fuel oil. Injection of the fuel into the combustionzone of a Dieselengine is not hindered by the colloidally suspendedactive sulfur which accelerates ignition of the fuel.

It is realized that in using the high sulfurcontaining substances ofthis invention, care must be taken especially with parts of apparatususually constructed of corrodible metals, such as zinc and copper, toavoid corrosion. Since the apparatus parts which usually contain thesemetals for flexibility are the fuel supply tanks and feedlines, caremight have to be taken to use more expensive non-corrosive metals inthese parts. But, in accordance with the present invention, thestable'active sulfur addition agents are readily adapted for addition tothe fuel at some convenien t point just prior to the introduction of thefuel into the combustion chamber, as for example, at the fuel linefilter so that the supply tank and fuel line for the most part are notcontacted by the high-sulf ur containing agent. The promoter in a solidstate, such as flowers of sulfur or crushed roll sulfur, may bemaintained in'a reservoir through which the oil passes for injectioninto the combustion zone, and the fuel oil will dissolve the promoter tothe extent desired. The rate of solution may be increased by theapplication of heat, which may be readily supplied from the engine, as,for example, from exhaust gases to the fuel or the promoter reservoir.By placing the solid addition agent reservoir in a by-pass of the fuelline near the engine, the amount of hydrocarbon fuel passed into contactwith the agent for bringing it into solution can be regulated.

This method of dissolving into the oil or passage to the engine desiredamounts of a slightly soluble normally solid Diesel fuel ignitionpromoter is particularly advantageous for high sulfur-containingpromoters which may tend to corrode supply tanks and fuel lines made ofmetals which do not resist sulfur corrosion. But this method has otheradvantages in utilizing normally solid and slightly soluble promoters.For instance, it avoids troubles from. deterioration and separation ofsuch an agent which might arise from long standing and exposure to .airand moisture of fuel containing the agent, and it permits betteradaptation of the fuel for any particular engine and at any time of theengines operation, since engines have difierent sensitivities toignition qualities and ignition quality improvement is more necessarywhen starting a cold engine than in a heated r unning engine.

Owing to the good stability to heat, air, and.

' tions of about .025 to 1 or 2%.

solution of the agent.

moisture of ignition accelerating sulfur in the free and combined formsdescribed, not only are these materials suitable agents for addition toa fuel on its passage through a fuel line to the engine but also to afuel containing heat received in a processing step. For example, thesestable agents may be dissolved into a hot hydrocarbon distillate as thedistillate is being condensed in a fractionating tower or be added atsome convenient point in a withdrawal 'line where the distillate issufficiently hot to aid the This method of adding the agent to the fuelis advantageous for conserving heatand for efii'cient handling ofmaterials.

The proportion of ignition quality improving agent to be added to ahydrocarbon fuel ranges from a fraction of 1% to the limit of solubilityin the fuel, and, as needed, free sulfur. Although free sulfur dissolvesin some hydrocarbon fuels in concentrations as high as about 2 to 3%, ismay be preferably used in concentra- When combined or associated withphosphorus or amino groups, the thus modified sulfur may be preferablyused in concentrations from about .025 to 5%. A gas oil boiling fromabout 400 F. to 700 F. or 750 F.,

or, in general, having a suitable boiling range and viscosity for use asa fuel in Diesel type engines, may be used as the hydrocarbon fuel.Under some circumstances, a more narrowly cut fraction, such as onedistilling from 400 to 600 F. or from 500 to 700 F. may be used,Ordinarily, the hydrocarbon fuel may be said to have a boiling rangeabove that of gasoline. I

This invention makes commercially feasible the preparation of Dieselfuels giving satisfactory engine performance from crude oils, gas oils,and residual fuels having low pour points, low A. P. I. gravities, andhigh heat values, such oils being procured from naphthene base, asphaltbase, or mixed base stocks. Heavier and lower grades of petroleum oil,such as residual oils, are even made more suitable for slow speedengines.

The burning qualities of fractions from paraffin crudes or hydrogenatedoils are also enhanced by the novel addition agent of this invention.

Small quantities of these novel addition agents may be used for adaptingvarious mixtures of hydrocarbons for use as Diesel fuels, includingrecycle stocks from cracking operations, nonparafinicextracts, oils fromdestructive distillations of pyro-bituminous and asphaltic materials,and mixtures of these with one another or with crude petroleumfractions. With improvement in the ignition qualities of the hydrocarbonfuels mentioned by addition of inexpensive agents herein disclosedbetter performance of a Diesel engine operating on the improved fuel isobtained in the way of easier starting, smoother idling, silent running,and absence of shock loading.

It is not intended that this invention be limited to the specificexamples which are given merely for the sake of illustration, but it isdesired to claim all the novelty inherent in this invention in theappended claims as broadly as the prior art permits.

Other agents for enhancing various other qualities without detractingsubstantially from the ignition qualities of the fuel may be admixed,such as oiliness agents, sludge dispefsers, colloidal suspensiondispersers and stabilizers, dyes, antioxidants, viscosity improvers,pour point depressants, solubilizers, gum solvents, and corrosioninhibitors. Substances such as oleiines, amines, and peroxides may bementioned as being effective for reducing any corrosive tendencies ofactive sulfur promoters. Also, other promoters of ignition quality maybe admixed, particularly alkyl nitrates, such as amyl nitrate.

We claim:

1. A fuel for compression-ignition engines of the Diesel type comprisinga liquid hydrocarbon Diesel fuel boiling above 400 F. and an added smallproportion of sulfur in a free and loosely combined form to improvesubstantially ignition qualities of the fuel, free sulfur being added inan amount above 0.025%.

2. A fuel as described in claim 1 in which added sulfur is looselycombined in substantially molecular additive form with amino groups.

3. A fuel as described in claim 1 in which the sulfur is partly combinedwith phosphorus.

4. A fuel for compression-ignition engines of the Diesel type comprisinga liquid hydrocarbon Diesel fuel boiling above 400 F. and a small amountof added free sulfur above 0.025% to improve substantially ignitionqualities of the fuel.

5. A compression-ignition engine fuel com- 1,.

prising a hydrogenated hydrocarbon oil boiling in 8. Diesel fuel rangeand from to about 1% of dispersed free sulfur addedin small andsufflcient amounts for promoting ignition of the fuel to a substantialdegree.

6. A fuel for combustion engines of the Diesel type comprising a liquidhydrocarbon Diesel fuel and a small amount of a high sulfur containingignition promoter in which sulfur is combined with amino groups in theratio required to form hexasulfamide with which above 0.025% of freesulfur is incorporated in the fuel.

'7.- A fuel for compression ignition engines of the Diesel typecomprising a liquid hydrocarbon Diesel fuel and a small amount of a highsulfurcontaining ignition-promoter in which sulfur is combined withphosphorus in the ratio required to form phosphorus sesquisulfide withwhich at least 0.025% of free sulfur is incorporated in the fuel.

8. Method of preparing a Diesel fuel of improved ignition qualitieswhich comprises treating a crude petroleum oil Diesel fuel distillate,boiling above about 400 F., to disperse therein a suflieient amount offree sulfur to improve substantially ignition qualities of the fuel fromto about 1% of free sulfur being incorporated into the treated fuel.

9. A method of accelerating ignition of a fuel for combustion in enginesof the Diesel type which comprises incorporating into a liquidhydrocarbon Diesel fuel boiling above about 400 F. prior to ignition asufficient amount of free sulfur above 0.025% to improve substantiallyignition qualities of the fuel.

10. A fuel for compression-ignition engines comprising a majorproportion of a liquid bydrocarbon Diesel fuel boiling above about 400F. and a minor proportion of sulfur partly in the form of free sulfurand partly in the combined form of hexasulfamide, the free sulfur beingadded in an amount above0.025% to substantially raise the cetane numberof the fuel.

11. A fuel for compression-ignition engines comprising a majorproportion of a liquid hydrocarbon Diesel fuelboiling above about 400 F.and a minor proportion of sulfur partly in the form of free sulfur andpartly in the combined form of phosphorus sesquisulfide, the free sulfurbeing added in an amount above 0.025% to substantially raise the cetanenumber of the fuel.

PHARIS MILLER. GOULD H. CLOUD.

